The present invention relates to a vulcanizing adhesive composition, and more particularly to a vulcanizing adhesive composition effectively applicable to bonding of fluororubber to a metal, etc.
Most of silane-based adhesives for fluororubber so far used contain an organic solvent harmful to human bodies or global environments. JP-A-5-86335 on the other hand discloses an aqueous adhesive composition comprising an alkoxysilane compound and an unsaturated acid compound, but the wettability toward metals is not good with poor adhesiveness; and its adhesiveness is satisfactory only for polyol-vulcanizable fluororubber, but not for peroxide-vulcanizable fluororubber.
An object of the present invention is to provide an aqueous vulucanizing adhesive composition free from any organic solvent and effectively applicable to both polyol-vulcanizable fluororubber and peroxide-vulcanizable fluororubber, and also showing an effective adhesiveness to stainless steel to which the conventional aqueous adhesives have shown a poor adhesiveness.
The object of the present invention can be attained by a vulcanizing adhesive composition, which comprises a copolymerization oligomer of amino group-containing alkoxysilane and vinyl group-containing alkoxysilane, a nonionic surfactant of HLB 10-16, and an acid compound.
Amino group-containing alkoxysilane for use in the present invention as one component for the copolymerization oligomer includes, for example, xcex3-aminopropyltriethoxysilane, xcex3-aminopropyltrimethoxysilane, N-xcex2-(aminoethyl)-xcex3-aminopropyltrimethoxysilane, N-xcex2-(aminoethyl)-xcex2-aminopropyltriethoxysilane, etc. These amino group-containing alkoxysilanes, when used directly as a member of the adhesive composition, fail to give a good adhesive because no satisfactory film can be obtained, and thus are used in the form of copolymerization oligomers with vinyl group-containing alkoxysilanes.
Vinyl group-containing alkoxysilane for use in the present invention as another component of the copolymerization oligomer includes, for example, vinyltrimethoxysilane, vinyltriethoxysilane, etc. The vinyl group-containing alkoxysilanes are insoluble in water, separable as an oil layer and immiscible with other components. Their oligomers are also insoluble in water to form precipitates. Thus, the vinyl group-containing alkoxysilanes are used as oligomers with amino group-containing alkoxysilanes.
In the oligomerization reaction, 0.2-1 mole, preferably 0.5-1 mole, of vinyl group-containing alkoxy-silane and 1-5 moles of water are used per mole of amino group-containing alkoxysilane. These components are charged into a reactor with a distillation apparatus and a stirrer and stirred at about 60xc2x0 C. for about one hour. Then, about 1- about 2 moles of an acid, for example, formic acid, is added thereto per mole of amino group-containing alkoxysilane within one hour, where the temperature is kept at about 65xc2x0 C. . Then, stirring is continued for 1-5 hours to proceed with the reaction, while distilling off alcohol resulting from hydrolysis under reduced pressure. The distillation is discontinued when the distillate turns only water. Then, the desired copolymerization oligomers can be obtained by adjusting the silane concentration to 30-80 wt. % by dilution. Alternatively, commercially available copolymerization oligomers can be used as such.
Any of nonionic surfactants can be used, but it is preferable to use those having HLB 10-16, preferably 12-14, for example, polyoxyethylene alkyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene fatty acid ester, etc. Those of lower HLB than 10 are insoluble in water, making the solution white turbid, whereas those of higher HLB than 16 have a poor effect on wettability improvement. Acid compound for use in the present invention includes an organic acid such as formic acid, acetic acid, etc. and an inorganic acid such as hydrochloric acid, nitric acid, etc.
In addition to the foregoing component, an amino group-containing alkoxysilane oligomer can be used together with the amino/vinyl group-containing alkoxy-silane copolymerization oligomer to reduce the proportion of the latter to be used. In that case, it is necessary to add an acid compound dropwise to the amino group-containing alkoxysilane oligomer in advance to make pH to 4-5. The amino group-containing alkoxysilane oligomer can be obtained by charging one mole of an amino group-containing alkoxysilane and 5-50 moles of distilled water into a reactor with a distillation apparatus and a stirrer, followed by stirring at about 40xc2x0- about 60xc2x0 C. for about 5- about 48 hours to proceed with the reaction, while distilling off alcohol resulting from hydrolysis under reduced pressure. Alternatively, commercially available oligomer products can be used as such. The amino group-containing alkoxysilane oligomer can be used in a proportion of not more than about 10 parts by weight, preferably about 0.5- about 3 parts by weight on the basis of one part by weight of the copolymerization oligomer.
The present vulcanizing adhesive composition can be prepared by diluting the copolymerization oligomer to a concentration of about 0.5- about 10%, preferably about 1- about 5%, by distilled water, and adding a nonionic surfactant and an acid compound to make about 0.01- about 0.5%, preferably about 0.05- about 0.2%, and about 0.1- about 5%, preferably about 0.2- about 1%, respectively, on the basis of the entire composition, followed by stirring for a few minutes.
The vulcanizing adhesive composition thus prepared can be effectively used in the vulcanization bonding between fluororubber and metals, etc. That is, the composition is applied to a metal such as mild steel, stainless steel, aluminum, aluminum die-cast, etc., dried at room temperature- about 80xc2x0 C. for about 2- about 10 minutes and baked at about 100xc2x0- about 200xc2x0 C. for about 5- about 10 minutes, thereby bonding unvulanized fluororubber compounds thereto, followed by vulcanization under pressure at about 180xc2x0- about 200xc2x0 C. .
Any of polyol-vulcanizable fluororubber and peroxide-vulcanizable fluororubber can be used, and unvulcanized fluororubber compounds include, for example, the following formulations:
Polyol-vulcanizable fluororubber generally includes copolymers of vinylidene fluoride with at least one of other fluorine-containing olefins such as hexa-fluoropropene, pentafluoropropene, tetrafluoroethylene, trifluorochloroethylene, vinyl fluoride, perfluoro (methyl vinyl ether), etc., and these fluororubbers can be polyol-vulcanized by a polyhydroxy-aromatic compound such as 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) perfluoropropane, hydroquinone, etc.
Peroxide-vulcanizable fluororubber includes fluoro-rubbers containing iodine and/or bromine in the molecule, and these fluororubbers can be vulcanized (cross-linked) by an organic peroxide so for usually used in the peroxide vulcanization. In that case, it is preferable to use a multifunctional unsaturated compound typified by triallyl isocyanurate together with the organic peroxide.
The present invention will be described below, referring to Examples.